Control of detonative cleaning apparatus

ABSTRACT

An apparatus is provided for cleaning one or more surfaces within a vessel having a vessel wall separating a vessel exterior from a vessel interior and having a wall aperture. The apparatus has at least one elongate conduit having an upstream first end and a downstream second end and positioned to direct a shockwave from the second end into the vessel interior. A source of fuel and oxidizer is coupled to the conduit to deliver the fuel and oxidizer to the conduit An initiator is positioned to initiate a reaction of the fuel and oxidizer to produce the shockwave. At least one sensor coupled to the conduit to detect motion indicative of a detonation. A control system coupled to the initiator, the source, and the sensor for receiving input from the sensor and controlling operation of the initiator and source responsive to said input.

BACKGROUND

The disclosure relates to industrial equipment. More particularly, the disclosure relates to the detonative cleaning of industrial equipment.

Surface fouling is a major problem in industrial equipment. Such equipment includes furnaces (coal, oil, waste, etc.), boilers, gasifiers, reactors, heat exchangers, and the like. Typically the equipment involves a vessel containing internal heat transfer surfaces that are subjected to fouling by accumulating particulate such as soot, ash, and minerals, more integrated buildup such as slag and/or fouling, and the like. Such particulate build-up may progressively interfere with plant operation, reducing efficiency and throughput and potentially causing damage. Cleaning of the equipment is therefore highly desirable and is attended by a number of relevant considerations. Often direct access to the fouled surfaces is difficult. Additionally, to maintain revenue it is desirable to minimize downtime associated with cleaning. A variety of technologies have been proposed.

An exemplary detonative cleaning apparatus includes a conduit into which fuel and oxidizer are introduces and then ignited. The ignition causes a shock wave to be discharged from the conduit to impact the surfaces to be cleaned. By way of example, U.S. patent application publication 20050199743, the disclosure of which is incorporated herein by reference in its entirety as if set forth at length, discloses a detonative cleaning apparatus control system and has a specific illustration relative to a segmented conduit assembly. Alternative apparatus are of the retractable lance-type. Such systems are often identified as “soot blowers” after the key application for the technology.

SUMMARY

One aspect of the disclosure involves an apparatus for cleaning one or more surfaces within a vessel having a vessel wall separating a vessel exterior from a vessel interior and having a wall aperture. The apparatus has at least one elongate conduit having an upstream first end and a downstream second end and positioned to direct a shockwave from the second end into the vessel interior. A source of fuel and oxidizer is coupled to the conduit to deliver the fuel and oxidizer to the conduit An initiator is positioned to initiate a reaction of the fuel and oxidizer to produce the shockwave. At least one sensor coupled to the conduit to detect motion characteristic of a detonation. A control system coupled to the initiator, the source, and the sensor for receiving input from the sensor and controlling operation of the initiator and source responsive to said input.

The details of one or more embodiments of are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of an industrial furnace associated with several soot blowers positioned to clean a level of the furnace.

FIG. 2 is a side view of one of the blowers of FIG. 1.

FIG. 3 is a schematic view of a control system for multiple cleaning apparatus.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows a furnace 20 having an exemplary three associated soot blowers 22. In the illustrated embodiment, the furnace vessel is formed as a right parallelepiped and the soot blowers are all associated with a single common wall 24 of the vessel and are positioned at like height along the wall. Other configurations are possible (e.g., a single soot blower, one or more soot blowers on each of multiple levels, and the like).

Each soot blower 22 includes an elongate combustion conduit 26 extending from an upstream (e.g., distal/inlet) end 28 away from the furnace wall 24 to a downstream (e.g., proximal/outlet) end 30 closely associated with the wall 24. Optionally, however, the end 30 may be well within the furnace. In operation of each soot blower, combustion of a fuel/oxidizer mixture within the conduit 26 is initiated proximate the upstream end (e.g., within an upstreammost 10% of a conduit length) to produce a detonation wave. The detonation wave is expelled from the downstream end as a shockwave along with associated combustion gases for cleaning surfaces within the interior volume of the furnace.

Each soot blower may be associated with a fuel/oxidizer source 32. Such source or one or more components thereof may be shared amongst the various soot blowers. An exemplary source includes a liquified or compressed gaseous fuel cylinder 34 and an oxygen cylinder 36 in respective containment structures 38 and 40. In the exemplary embodiment, the oxidizer is a first oxidizer such as essentially pure oxygen. A second oxidizer may be in the form of shop air delivered from a central air source 42. In the exemplary embodiment, air is stored in an air accumulator 44. Fuel, expanded from that in the cylinder 34 is generally stored in a fuel accumulator 46. Each exemplary source 32 is coupled to the associated conduit 26 by appropriate plumbing below. Similarly, each soot blower includes a spark box 50 for initiating combustion of the fuel oxidizer mixture and which, along with the source 32, is controlled by a control and monitoring system (discussed below).

FIG. 2 shows further details of an exemplary soot blower 22. The exemplary detonation conduit 26 is formed with a main body portion formed by a series of doubly flanged conduit sections or segments 60 arrayed from upstream to downstream and a downstream nozzle conduit section or segment 62 having a downstream portion 64 extending through an aperture 66 in the wall and ending in the downstream end or outlet 30 exposed to the furnace interior 68. The term nozzle is used broadly and does not require the presence of any aerodynamic contraction, expansion, or combination thereof. Exemplary conduit segment material is metallic (e.g., stainless steel). The outlet 30 may be located further within the furnace if appropriate support and cooling are provided. FIG. 2 further shows furnace interior tube bundles 70, the exterior surfaces of which are subject to fouling.

An overall length L between ends 28 and 30 may be 1-15 m, more narrowly, 5-15 m. A fuel/oxidizer charge may be introduced to the detonation conduit interior in a variety of ways. There may be one or more distinct fuel/oxidizer mixtures. Such mixture(s) may be premixed external to the detonation conduit, or may be mixed at or subsequent to introduction to the conduit. FIG. 2 shows conduit configured for distinct introduction of two distinct fuel/oxidizer combinations: a predetonator combination; and a main combination. In the exemplary embodiment, at an upstream first location, one or more predetonator fuel injection conduits 90 are coupled to one or more ports 92 in the conduit to define fuel injection ports. Similarly, one or more predetonator oxidizer conduits 94 may be coupled to oxidizer inlet ports 96. A purge gas conduit 98 may be similarly connected to a purge gas port 100 yet further upstream., An igniter/initiator 106 (e.g., a spark plug) may be located near the upstream end of the combustion conduit.

In the exemplary embodiment, a main fuel is carried by a number of main fuel conduits 112 and a main oxidizer is carried by one or more main oxidizer conduits 110. In exemplary embodiments, the fuels are hydrocarbons. In particular exemplary embodiments, both fuels are the same, drawn from a single fuel source but mixed with distinct oxidizers: essentially pure oxygen for the predetonator mixture; and air for the main mixture. Exemplary fuels useful in such a situation are propane, MAPP gas, or mixtures thereof. Other fuels are possible, including ethylene and liquid fuels (e.g., diesel, kerosene, and jet aviation fuels). The oxidizers can include mixtures such as air/oxygen mixtures of appropriate ratios to achieve desired main and/or predetonator charge chemistries. Further, monopropellant fuels having molecularly combined fuel and oxidizer components may be options.

In operation, at the beginning of a use cycle, the combustion conduit is initially empty except for the presence of air (or other purge gas). The predetonator fuel and oxidizer are then introduced through the associated ports to fill an upstream section (e.g., just beyond the main fuel/oxidizer ports). The predetonator fuel and oxidizer flows may then be shut off. An exemplary volume filled the predetonator fuel and oxidizer is 1-40%, more narrowly 1-20%, of the combustion conduit volume. The main fuel and oxidizer are then introduced, to substantially fill some fraction (e.g., 20-100%) of the remaining volume of the combustor conduit. The main fuel and oxidizer flows are then shut off. The prior introduction of predetonator fuel and oxidizer past the main fuel/oxidizer ports largely eliminates the risk of the formation of an air or other non-combustible slug between the predetonator and main charges. Such a slug could prevent migration of the combustion front between the two charges.

With the charges introduced, the spark box is triggered to provide a spark discharge of the initiator igniting the predetonator charge. The predetonator charge being selected for very fast combustion chemistry, the initial deflagration quickly transitions to a detonation within the segment 84 and producing a detonation wave. Once such a detonation wave occurs, it is effective to pass through the main charge which might, otherwise, have sufficiently slow chemistry to not detonate within the conduit of its own accord. The wave passes longitudinally downstream and emerges from the downstream end 30 as a shockwave within the furnace interior, impinging upon the surfaces to be cleaned and thermally and mechanically shocking to typically at least loosen the contamination. The wave will be followed by the expulsion of pressurized combustion products from the detonation conduit, the expelled products emerging as a jet from the downstream end 30 and further completing the cleaning process (e.g., removing the loosened material). After or overlapping such venting of combustion products, a purge gas (e.g., air from the same source providing the main oxidizer and/or nitrogen) is introduced through the purge port 100 to drive the final combustion products out and leave the detonation conduit filled with purge gas ready to repeat the cycle (either immediately or at a subsequent regular interval or at a subsequent irregular interval (which may be manually or automatically determined by the control and monitoring system)). Optionally, a baseline flow of the purge gas may be maintained between charge/discharge cycles so as to prevent gas and particulate from the furnace interior from infiltrating upstream and to assist in cooling of the detonation conduit.

The apparatus may be used in a wide variety of applications. By way of example, just within a typical coal-fired furnace, the apparatus may be applied to: the pendants or secondary superheaters, the convective pass (primary superheaters and the economizer bundles); air preheaters; selective catalyst removers (SCR) scrubbers; the baghouse or electrostatic precipitator; economizer hoppers; ash or other heat/accumulations whether on heat transfer surfaces or elsewhere, and the like. Similar possibilities exist within other applications including oil-fired furnaces, black liquor recovery boilers, biomass boilers, waste reclamation burners (trash burners), and the like.

A variety of systems may be provided for monitoring and/or controlling operation of the detonative cleaning apparatus. The implementation of any particular control and monitoring system may be influenced by the physical environment including the nature and configuration of the vessel and its surfaces and the arrangement of the combustion conduit(s). FIG. 3 schematically shows one of a number of levels of a vessel 200. At this level, a number of combustion conduits 202A-D are positioned. In the exemplary embodiment, downstream outlets of the conduits are positioned in the interior of the vessel and upstream ends are external to the vessel. Although shown straight, the conduits may have non-straight configurations to discharge shockwaves in desired locations with desired directions. Each conduit is closely associated with an interface module 204A-D which may provide local control of various operational parameters (e.g., including fuel and oxidizer introduction, purge and cooling gas introduction, initiation, and the like). Further details of an exemplary interface module are discussed below. The given vessel level may also include sensors 206, 207, and 208. However, the sensors need not be level-specific. Similarly, the conduits could be other than level-specific and other than oriented to discharge in parallel planes. The sensors may be conduit-specific (e.g., close to the outlet of a specific associated conduit or to the furnace surface cleaned by such conduit) or may be more generally located. The sensors may detect one or more of thermal conditions, pressures, flows, chemical conditions, and/or visual conditions. Exemplary sensor operation is discussed in further detail below.

For signal communication, the modules and sensors are coupled via communication lines 209 to a hub (e.g., ethernet) 210. In the exemplary embodiment, the sensors are coupled to the hub via the modules (e.g., coupled to the modules by communication or signal lines). For physical input (e.g., fuel, oxidizer, purge gas, coolant, power, and the like), the modules are coupled to a central supply unit 212 via fluid and power lines 213. The hub and supply unit may be level-specific, common, or some combination. The hub is coupled for signal communication (e.g., via network lines 215 such as a fiber optic line, Ethernet line, or the like) to a control and monitoring system 214 of the facility (e.g., a general purpose computer running control/monitoring software) which may be specific to the vessel or central to a group of vessels at a site (e.g., a given facility). The supply unit may similarly be coupled to the system 214 via the hub 210 or may exist independently. The system 214 is in communication with a remote control and monitoring system 216. The system 216 may be in secure communication with a number of systems 214 at a number of different sites. In such a situation, however, the system 216 may be colocated with one or more of those systems 214 and off-site of the others. The exemplary communication between the system 216 and systems 214 is via a wide area network 217 such as the internet. Alternative public and private networks or other communication systems may be used. The supply unit 212 may, itself, be fed from a remotely located tank farm 218 (e.g., a central tank farm of the facility) via lines 219 for supply of non-air gases and other fluids and from appropriate shop air and power sources (not shown) which may also be central sources of the facility). The system 214 may communicate with several central systems. For example, the system 216 may be a central system of a facility owner/operator communicating with systems 214 at various facilities of that owner/operator. A central system 223 may be a central system of a service vendor communicating with systems 214 of various facilities of various owners/operators either directly or via the systems 216. Based ultimately upon data provided by the sensors 206 and 208, the systems 214 may inform the system 223 that service or routine maintenance is necessary or otherwise appropriate (the decision being made at any of the systems 214, 216, or 223).

In the exemplary embodiment, an emergency control panel 220 is in close proximity to the system 214. The exemplary emergency control panel includes one or more status lights and one or more switches (e.g., red/green status lights and emergency kill switches for each conduit plus a master kill switch for all conduits). These are coupled by lines 222 extending to the individual interface modules. In the event of a control system failure which might prevent control (namely safing) of the conduits via the system 214 and hub 210, the kill switches may be tripped by a technician to safe the conduits (e.g., shut the fuel and oxidizer valves, disable the ignition, and the like, to safely shut down and/or disable the associated conduits). The interface modules themselves may be set up in a failsafe mode whereby a break in the associated line(s) 215 or 222 causes a module to transition to a safe mode.

The sensors 206 and/or 207 may also represent motion sensors used to sense conduit motion responsive to the combustive event. In particular, the sensors may be used to verify detonation, generally, and the magnitude/sufficiency of the detonation, in particular. An exemplary motion sensor is an accelerometer. An exemplary accelerometer is a piezoelectric sensor such as a ceramic shear accelerometer. Another exemplary sensor is a vibration sensor. An exemplary vibration sensor is a mercury-free mechanical vibration switch. Another exemplary sensor is a strain gauge. Such sensors do not need direct exposure to the conduit interior or vessel interior (although the microphone in particular may also be amenable to interior exposure for more direct measurement). Such sensors may be mounted on the conduit exterior without an associated aperture to the conduit interior. This can save complexity, sensor robustness, etc. Advantageous sensor positioning may be outside the vessel to limit sensor exposure to severe environments.

Exemplary sensor coupling is a series coupling of the sensors (or back end signal processing circuit) for a plurality (e.g., all) of the conduits. The series circuit may be normally closed. In the event of a detonation on any conduit, the sensor will toggle and the circuit will open. The signal processing circuit may be configured to hold the open circuit open long enough (e.g., greater than a second) for the controller to read. At this point, if a particular conduit was commanded to fire and the circuit doesn't open, the controller knows which conduit failed to detonate. After a pre-defined number of failures of a given conduit to successfully fire, the control system may alert the operator and takes that particular conduit offline (e.g., while allowing for continued operation of the remaining conduits).

Another option for the sensors 206 and/or 207 is a pressure switch (as distinguished from a continuous pressure sensor). The switch threshold may be selected in view of its positioning to correspond to a desired threshold for the pressure associated with detonation. Triggering of the switch would thus indicate a successful detonation, while a failure to trigger would indicate an unsucccessful or sub-threshold event. An exemplary positioning is in an upstream half of a length of the conduit.

Such sensing of the detonation (or lack thereof) may be combined with further control aspects and inputs such as are identified in the above-mentioned U.S. patent application publication 20050199743.

One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, the invention may be adapted for use with a variety of industrial equipment and with variety of soot blower technologies. For example, the principles may be adapted to various existing or yet-developed detonative cleaning apparatus, including fixed and extensible/retractable units. Aspects of the existing equipment and technologies may influence aspects of any particular implementation. Accordingly, other embodiments are within the scope of the following claims. 

1. An apparatus for cleaning one or more surfaces within a vessel having a vessel wall separating a vessel exterior from a vessel interior and having a wall aperture, the apparatus comprising: at least one elongate conduit having an upstream first end and a downstream second end and positioned to direct a shockwave from the second end into the vessel interior; and a source of fuel and oxidizer coupled to the conduit to deliver the fuel and oxidizer to the conduit; an initiator positioned to initiate a reaction of the fuel and oxidizer to produce the shockwave; at least one sensor coupled to the conduit to detect motion indicative of a detonation; and a control system coupled to the initiator, the source, and the sensor for receiving input from the sensor and controlling operation of the initiator and source responsive to said input.
 2. The apparatus of claim 1 wherein: the sensor is a piezoelectric sensor.
 3. The apparatus of claim 1 wherein: the sensor is a contact accelerometer.
 4. The apparatus of claim 1 wherein: the sensor is a contact vibration sensor.
 5. The apparatus of claim 1 wherein: the sensor is in contact with an exterior of the conduit without an associated aperture to the interior of the conduit.
 6. The apparatus of claim 1 wherein: there are a plurality of such conduits and such initiators, each of the conduits associated with an associated one or more of the initiators; and the sensors are series coupled to the control system.
 7. The apparatus of claim 6 wherein: the control system is programmed to generate maintenance or service requests responsive to the input.
 8. The apparatus of claim 6 wherein: the control system is programmed to determine detonation failures of the conduits individually.
 9. The apparatus of claim 8 wherein: the control system is programmed to individually adjust operational parameters of the conduits responsive to the determined failures.
 10. The apparatus of claim 1 wherein: the control system communicates with a remote monitoring system.
 11. The apparatus of claim 1 wherein: the control system is programmed to determine a detonation success or failure status.
 12. The apparatus of claim 1 wherein: the control system is programmed with a plurality of different cleaning processes and to execute the processes responsive to corresponding sensed conditions.
 13. A method for cleaning a surface within a vessel, the method comprising: introducing fuel and oxidizer to at least one elongate conduit having an upstream first end and a downstream second end and positioned to direct a shockwave from the second end into the vessel interior; initiating a reaction of the fuel and oxidizer; detecting a motion of the conduit; responsive to the detecting, determining a characteristic of the reaction; and responsive to the determined characteristic, adjusting at least one parameter of the introducing and initiating so as to provide feedback control of the characteristic.
 14. The method of claim 13 wherein: the detecting comprises detecting an acceleration.
 15. The method of claim 13 wherein: the detecting comprises detecting a vibration parameter.
 16. The method of claim 13 wherein: the determining comprises determining a sufficiency of a detonation.
 17. The method of claim 13 further comprising: responsive to the determined characteristic, generating an automated maintenance or service request.
 18. An apparatus for cleaning one or more surfaces within a vessel having a vessel wall separating a vessel exterior from a vessel interior and having a wall aperture, the apparatus comprising: at least one elongate conduit having an upstream first end and a downstream second end and positioned to direct a shockwave from the second end into the vessel interior; and a source of fuel and oxidizer coupled to the conduit to deliver the fuel and oxidizer to the conduit; an initiator positioned to initiate a reaction of the fuel and oxidizer to produce the shockwave; a pressure switch coupled to the conduit to be exposed to pressure associated with the reaction; and a control system coupled to the initiator, the source, and the pressure switch for receiving input from the pressure switch and controlling operation of the initiator and source responsive to said input.
 19. The apparatus of claim 18 wherein the pressure switch is a binary switch, with an open condition associated with pressure below a threshold and a closed condition associated with pressure above the threshold.
 20. The apparatus of claim 18 wherein the pressure switch is along an upstream half of a length of the conduit. 